In general, a galvanized steel sheet with high corrosion resistance is sometimes used in suspension parts relevant to wheels that are an automotive component, or in underbody parts that are a portion facing the road surface in an automotive body. For example, in a suspension member or a suspension arm, which is an automotive suspension parts, a galvanized steel sheet is used. The galvanized steel sheet used is often subjected to welding and is coated after the welding.
In the welding of a galvanized steel sheet, zinc is vaporized due to arc heat, and zinc vapor generated here may pass through a molten metal or be partially taken in by a molten metal, resulting in blowhole formation. As the amount of blowholes generated is larger, in the welding of a galvanized steel sheet, the blowhole resistance is judged to be poorer.
Various proposals for addressing the problem of the blowhole resistance have been heretofore made. For example, Patent Document 1 describes a technique of performing while shaking the weld pool and promoting discharge of zinc vapor, by controlling the waveform of welding current, setting the carbon dioxide gas concentration of a shielding gas to be relatively high, and repeating a high pulse current term and a low pulse current term.
In addition, Patent Document 2 describes a galvanized steel sheet, in which welding is performed at a high speed by periodically repeating a term in which a rectangular wave pulse is applied, and a term in which only a base current is applied.